Old thread, I know, but in case someone stumbles across this through the search I thought I?d add a little update.
Making a notch in the end of a small punch is a very good thing and the trick will assist greatly. I could not, however, hold the spring while trying to align the ejector assembly.
I instead just started the assembly to get it aligned in its cutout and THEN poked the punch through the assembly hole. At that point is pretty easy to feel the spring and much less likely to slip from the punch face. In fact I found this the EASIEST part of the whole reassembly!
Ashburnarmorers videos were both really good at explaining how the whole thing actually works and a very good guide.